This invention relates to metals having a silvery-white appearance and method of making the same, and, in particular to such metals produced by electroplating processes.
Nickel is used for a variety of different coinage, tokens, and medallions. More specifically, coinage, tokens, and medallions are often made with cupronickel, nickel brass, and nickel-plated steel. Cupronickel is also known as copper alloy C713,and contains 23.5% to 26.5% nickel by weight, with the balance of the composition comprising copper. One characteristic of nickel is its silvery-white appearance which is recognizable in distinguishing the nickel-based coinage, tokens, and medallions from other coinage, tokens, and medallions.
Many people have an allergy to nickel metals. Allergic reactions to nickel are not only a problem for consumers handling nickel-based objects, but are particularly a problem for persons, such as cashiers and tellers, who handle lots of coins, and for persons involved in the manufacture of such objects. Thus, it is desired to provide coinage, tokens, and medallions that do not expose such persons to nickel metals when in contact with the coinage, tokens, or medallions. Yet, if it is desired to modify coins, tokens, or medallions to eliminate contact to nickel metals, it is still desired to retain the silvery-white appearance for recognition and distinguishing purposes. For example, it is desired that any replacement for the 5 cent coin in the United States, known as the “nickel”, should have substantially the same appearance as the present-day “nickel”.
Present technology used to produce silvery-white coins, tokens, and medallions include: (1) A corrosion-resistant white metal alloy (stainless steel, nickel alloy, cupronickel, etc.); (2) A clad material with a corrosion-resistant white metal alloy bonded to a base metal core; and (3) Electroplated nickel over a base metal core (usually steel), often with one or more plated layers beneath the nickel. On steel, a total minimum plating thickness of 25 μm is usually specified, due to corrosion concerns. After plating, nickel-plated blanks must be baked to relieve the stresses in the plating, which would otherwise lead to cracking during the coining process. The oxides formed during this baking process must be removed by burnishing the blanks. In all three processes, the finished blank is capable of inducing contact dermatitis in any individual who is sensitized to nickel, unless the surface alloy contains no nickel.
In addition to maintenance of appearance, there are several other characteristics and properties required of coinage, tokens, and medallions. Over long usage, the coinage, token, or medallion must maintain its color, and be tarnish-resistant, durable, and attractive. The coinage, token, or medallion must stand up to the wear and tear of its intended usage and handling. Weight of the coinage, token or medallion is also a concern, particularly when used in automatic machines. For example, vending machines accepting coinage are often weight sensitive, as are machines accepting subway tokens.
It is also desired that any coinage, token, or medallion that does not expose a handler to any nickel metal also be comprised of materials and made by processes that are near or less the cost of materials and manufacture of present coinage, tokens, and medallions. No change in appearance should result in the finished product, and, therefore, such coinage, tokens, and medallions need to be able to be converted from a blank to a finished product using standard production techniques. Stated another way, the object must be fabricable into the end product and have sufficient ductility to enable it to be struck or minted into the finished product.
It is further desired to develop coinage, tokens, and medallions that are comprised of inexpensive metals—at least in part. For coinage, in particular, it is generally desired that the cost of the metal(s) and production for a coin be low relative to the face value of the coin. The less expensive the coin is to produce, the greater seigniorage is gained by the minting process. Further, if the value of the metal(s) of the coin exceeds the face value, the issuing entity will likely be forced to change the size or makeup of the coin to lower the value of the metal(s) in the coin so that the public will not sell the coins for the value of the metal(s). Consider, for example, the coin of U.S. Pat. No. 6,383,657 that has a silver appearance but does not utilize a silver core or silver cladding layers. Instead, aluminum and zinc are used to produce a coin having a silver appearance. Aluminum and zinc are both significantly less expensive materials than is silver.
Various efforts have been made in the past to make coinage, tokens, or medallions from alternate materials. For example, the invention of U.S. Pat. No. 5,151,167 comprises a coin including a blank electroplated with nickel, followed by an electroplated copper layer, and a final electroplated nickel layer. The invention of U.S. Pat. No. 5,151,167 does not require the use of nickel as the core of the coin, but, it results in a coin having nickel metals to which persons would be exposed. Thus, such a coin does not address the issue of nickel allergies. Also, the manufacture of the coin of U.S. Pat. No. 5,151,167 involves three electroplating processes to result in the “nickel” coin, and is therefore expensive to perform.
Several methods have been developed to produce coins having a golden color. For example, U.S. Pat. No. 4,579,761 describes production of coins having a gold appearance by using yellow bronze. The yellow bronze of U.S. Pat. No. 4,579,761 contains 8% to 16% by weight of tin, with the balance as copper. Similarly, U.S. Pat. No. 6,432,556 discloses production of a coin having a golden appearance. The coin includes two cladding layers. The first cladding layer contains 6% to 12% manganese and 6% to 25% zinc, while the second cladding layer contains 7% to 10% manganese and 10% to 15% zinc. U.S. Pat. No. 6,432,556 also suggests that the cladding layers might contain nickel, and could contain small traces of other metals, such as tin. These patents teach one skilled in the art to produce coins having a gold appearance—not a silvery-white appearance as results in the use of nickel.